Damage to the anterior and/or posterior cruciate ligament and the capsule of the knee is common following trauma to the knee such as can be experienced skiing, playing football and in motor vehicle accidents to name but a few. Currently subjective interpretation of the unstable knee is made by the Orthopaedic surgeon attending the patient using a manual test such as the Lachman test. This estimation is made pre- and post-operatively and varies with the amount of force used by the surgeon in the examination. Estimating capsular laxity as opposed to cruciate ligament rupture, which has implications for the necessity of operation, is very difficult using this method.
A number of attempts have been made in the past to produce devices to objectively measure anterior and/or posterior cruciate ligament rupture. These attempts are summarized in U.S. patent specification No. 4,583,555 which itself discloses a device for this purpose. The present inventors have found that all of these prior art proposals suffer from the deficiency that they do not produce an indication of the amount of relative displacement between the femur and the tibia at a plurality of different applied forces. The present inventors provide a device which gives, in preferred embodiments, a plot of relative displacement between the femur and the tibia against an actively applied force i.e., a force applied by the patient rather than the surgeon conducting the examination.